1. Field of the Invention
The present invention relates to a circuit for detecting a wobble signal from various kinds of media having different pre-formats.
2. Description of the Related Art
A general recording medium employs a pre-format in which a wobble signal frequency detectable from deviation of tracks formed on the medium becomes constant when constant linear velocity (CLV) rotation control is performed in order to detect a linear velocity at a radial position accurately. A detailed description of the wobble signal will be given later.
The wobble signal frequency differs depending on the pre-format. For example, CD, DVD-RAM, and DVD-R have different wobble signal frequencies. Additionally, physical address information is also necessary so as to identify an approximate position in an unrecorded area. However, the physical address information is obtained by different method depending on the pre-format. For example, the physical address information is obtained by performing frequency modulation to the wobble signals in a CD, by prepits in a DVD-RAM, and by land prepits formed between tracks in a DVD-R.
A simple method to cope with a plurality of media having different pre-formats is to carry detection circuits exclusive for respective pre-formats in parallel and to select the detection circuit depending on the pre-format of the medium to be accessed.
In Japanese Laid-Open Patent Application No. 2000-207745 “Wobble Clock Generating Circuit and Optical Disc Apparatus Using the Same”, two or more filter circuits are provided so as to select the filter suitable for the wobble signal that changes frequency according to rotational errors of a spindle motor.
As in the case of the above-mentioned publication, there is a case where a plurality of the filter circuits are carried in parallel even for one formatted medium and the suitable filter circuit is selected and used. A structure in the above-mentioned case is for preventing performance of the wobble signal detection from deteriorating due to change of rotational velocity of the medium.
Thus, in an apparatus which records on and reproduces a plurality of the media having various pre-formats, when the wobble detection circuits exclusive for respective pre-formats are provided or when, as in the above publication, a plurality of filter circuits are carried in parallel for one pre-format medium, the circuit size becomes very large. Accordingly, power consumption increases and it becomes difficult to reduce the circuit size.